Typically a reflector for an automotive lighting element will have a curved shape which may, for example, be parabolic, ellipsoidal or homofocal, in order to provide a reasonably collimated or directed beam of light from the light emitted by the light bulb. Sometimes, for reasons of styling, portions of the reflector will be essentially flat rather than curved. When the bottom portion of the reflector is flat a dangerous situation is created. The danger results from the fact that light reflected off of the flat bottom of the reflector will not be collimated but will be reflected upward. If the lighting element in question is a rear-mounted lamp such as a taillamp or a center high-mounted stop lamp, some of the light will be reflected into the eyes of following drivers. If the lighting element in question is a front-mounted lamp such as a headlamp, some of the light will be reflected into the eyes of on-coming drivers. The danger of this situation is increased in headlamps which are aerodynamically designed with a sloping front. This increased danger arises from the fact that some of the light that would otherwise be intercepted by the upper reflector if the front lens was vertical is allowed to escape from the lamp.
One approach to solving this safety problem is to provide a non-reflecting surface to the lower portion of the reflector. There are two disadvantages inherent in this approach. The first disadvantage is that the efficiency of the lighting element is reduced because the light striking the non-reflecting surface will be absorbed rather than reflected. Second, the darkened surface in the headlight provides an appearance that is less desirable than the highly reflective surface normally present.
Another approach is the use of a bulb shield which prevents light from striking the flat surface. Such shields provide an undesirable appearance when the light source is turned off and creates a shadow in the light beam when the light source is turned on.